Dielectric recording on insulator surfaces

ABSTRACT

A method is provided for effecting dielectric recording on insulator surfaces. The image is formed on an insulator sheet by varying imagewise the dielectric characteristics of the insulator sheet, and then applying a charge through the sheet from one side of the sheet while developing the other side of the sheet.

United States Patent 1191 Metcalfe et a1.

[ Apr. 16, 1974 DIELECTRIC RECORDING 0N HNSULATOR SURFACES Inventors: Kenneth A. Metcalfe, Lockleys;

William H. Lowe, Beaumont, both of Australia Assignee: The Commonwealth of Australia Filed: Aug. 16, 1971 Appl. No.: 172,084

Foreign Application Priority Date Aug. 17, 1970 Australia 2215/70 Aug. 16, 1971 Australia 32375/71 References Cited UNITED STATES PATENTS Goffe 355/17 2,758,525 8/1956 Moncrieff-Yeates 117/l7 5 1,784,912 12/1930 Scott 117/17.5 3,518,081 6/1970 Bickmore et al. 117/l7.5 3,569,803 3/1971 Sato et a1 355/17 3,427,242 2/1969 Mihajlov 117/37 LE 3,615,383 10/1971 Inoue 117/37 LE 3,383,993 5/1968 Yeh 117/37 LE 3,384,565 5/1968 Tulagin et a1 117/37 LE 3,384,566 5/1968 Clark 117/37 LE 3,527,684 9/1970 York et a1 117/37 LE Primary Examiner-Michael Katz Assistant ExaminerM. Sofocleous Attorney, Agent, or Firm-Eric H. Waters [57] ABSTRACT A method is provided for effecting dielectric record ing on insulator surfaces. The image is formed on an insulator sheet by varying imagewise the dielectric characteristics of the insulator sheet, and then applying a charge through the sheet from one side of the sheet while developing the other side of the sheet.

19 Claims, 5 Drawing Figures I /ns1//a//'0n 5668/ /l DIELECTRIC RECORDING N HNSIULATOR SURFACES This invention relates to a method of and means for effecting dielectric recording on insulator surfaces.

STATE OF THE ART In cases where it is necessary or desirable to record information for transmission or for producing facsimiles dielectrically on a heterogeneous insulator matrix, certain difficulties have occurred in the past in that it is generally necessary to apply a charge to the surface on which the image is contained, and then to either use some method of modifying this charge to allow development of the potential difference to take place, or else it is necessary to contact the surface with members or stylii to which a voltage is applied to produce on the surface the necessary charge of therequired pattern, and to then develop this image xerographically by the attraction to the latent image on the insulator medium of the marking component of the developer.

There are a number of difficulties where purely xerographic methods are used for this particular type of image production because in such a case the production of the initial signal, as well as development of the signal, is dependent on the attraction to the latent image of the developer and, where charging of insulator surfaces is involved, considerable difficulties occur through lateral flow of the charges, and through artifacts caused by Lichtenberg figures and the like.

To understand some of the problems in applying charges to insulator surfaces, and maintaining them, and subsequently developing the same, some consideration should be given to the problems which are met in xerographic processes.

When using photoconductors, the surface is generally charged and then modified imagewise by electromagnetic waves, such as light or X-rays, to bleed away the charges in those areas where the photoconductor was rendered conductive by the electromagnetic waves but the effectiveness of an image is subject to problems of charge generation and retention at uniform levels, the loss or variation of which results in loss of uniformity in an image subsequently developed.

Lateral flow of the charges tends to occur, particularly where there are delays between production of an image and subsequent development, and difficulties occur in uniform charge application.

Also there is a tendency for the produced image fields to be intensified at the edges of charge retaining areas, partly due to charge flow because of repelling polarities, producing what is commonly known as lack of infill. This problem is particularly troublesome when developing continuous tone images, and many systems at present in use suffer from the inability to reproduce such images, limiting the operation in many instances to the copying of relatively thin-line material such as typed pages where charge migration effects are not so noticeable.

With the advent of more sensitive liquid developers, that is developers in which marking particles are suspended in an insulating liquidso that the marking particles can develop an inherent charge of a selected polarity on their surface, the problems of lack of infill is reduced because particles, particularly if the surface charged on the particles is controlled by a control agent applied to the marking particles, can then be selected to develop even weaker charge areas so that by maintaining development the required infill is obtained, even between the stronger edge fields which exist.

Thus, in xerography, the charge must be of a particular polarity and varying imagewise on the surface, while the developer is of an opposite polarity when the charge on the surface is to be developed, or of a similar polarity when the background is to be developed, this latter being known as repulsion development.

It is also known according to the prior art that insulator surfaces can hold a charge, and an image applied thereto can be developed by applying marking particles, but again the effect is produced by holding a charge on an insulator surface in a patterned manner to produce an image. The charge is usually applied to such insulator surfaces by direct inscribing by means of a stylus held at a required potential, or by associating such an insulator sheet with a photoconductive medium on which an image is produced by for instance charging and light modifying the photoconductor surface and then transferring the electrostatic image to the insulating sheet.

Such charges are however again subject to lateral flow and Lichtenberg figures, as well as difficulty in transferring the charges without lateral distortion and consequent loss of definition.

To avoid charge loss or distortion on an insulator surface, it has been proposed to develop at the time that a writing point or stylus or the like applies the charge to the insulator surface, but this does not allow ready image production and development when considerable areas are involved.

An object of this invention is to produce an image on an insulator surface without image charge problems in spite of a delay between image formation and development.

SUMMARY OF THE INVENTION According to the present invention, instead of the image being produced in the form of a latent electrostatic image, it is produced by varying imagewise the dielectric characteristics of the insulator sheet, and then applying a charge through the sheet (which then has its dielectric constant modified in selected areas) while developing one side of it. Thus a uniform charge is applied from one side of the sheet while the developer is applied to the other side, the uniform applied charge being modified by the dielectric image to give an image modified field on the side to which the developer is applied.

While the developer may be moved to the image site by the polarity of the dielectrically modified field, development may take place by using a dielectric developer which is capable of emphasizing the differences in intensity of electric fields, regardless of the polarity of the fields.

In this respect it must be appreciated that developers using insulating medium or having an insulating control medium covering the marking particles, have an inherent charge polarity which insures polarity-wise development, but when using developers which are relatively conductive such as polar materials, the developer can develop by charge intensity as opposed to polarity because both polarities are present on the developer.

Thus, in the present invention, the method and means for recording information for transmission and for producing facsimiles dielectrically on a heterogeneous insulator matrix relates to applying a signal to the surface of the matrix to produce a local difference in dielectric properties through the surface, and the record so produced is then developed in a liquid developer to render the image permanent and visible, the characterizing feature of the present invention being that the image is produced in what may be termed amplified form by the application of a field such as from a charged insulator sheet or roller to the back surface of the recording sheet or matrix at the time of development, so that the image sheet itself is not required to hold a charge or have a charge applied thereto.

Thus the image sheet is a medium for modifying a charge applied through the image sheet at the time of development, so that the field is applied from means independent of the produced image on the image sheet, whereby amplification of the image field is achieved due to the application of the field to the back surface of the recording sheet or matrix.

The method, which as said has application in electrophotography, comprises first exposing the photoinsulator to light or X-rays in the presence of a photoconductive medium, or to a stylus with a potential thereon, to produce a difference in dielectric properties between the light exposed areas and the dark-adapted areas, or as modified by flow from the stylus, through the layer, in contra-distinction to applying it at the surface in conventional electrophotography, after which the layer is developed while a field such as from a triboelectrically charged insulator sheet or roller is applied to the back of the picture sheet. The method requires that the sheet and any backing it may have shall be insulating, as compared with the normal conducting backing essential for electrophotography where, without a conducting backing, it is not possible to bleed away the charge from the light struck areas, but an embedded photoconductor as envisaged arrests the modifying of the insulator dielectrically.

In its preferred form, the present invention requires that the developer shall be a dielectric developer capable of emphasizing differences in intensity of electric fields, regardless of sign, but the invention is seen as involving an image-sheet which serves as an imagewise gate to produce a dynamic field through the sheet, applied from the back, to control deposition of the developer particles.

By use of the present invention, electrophotographic machines may be simplified because the photo-sheet is not charged, and because the charging of the insulator which produces or amplifies the result is possible by merely using a rubbing member which generates static electricity on the insulator.

Any rubbing action on the insulator, or similar effect, which is to provide the charge during the development period can be used, and no high voltage generating apparatus or corona charging wires are necessary. A plate held at a required potential can however be used.

The type of developer used is preferably one which comprises conductive particles, or particles which are of a polar nature.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 (A) is a schematic view showing a homogeneous insulator sheet with an embedded photoconductor being subjected to light rays to produce the dielectric image;

FIG. 1 (B) shows how a backing sheet of insulating material may be charged by rubbing it with a brush;

FIG. 1 (C) shows how the insulator sheet with the dielectric image on it is then placed on the charged backing sheet and a developer roller applied to its upper side to develop the field which is then induced imagewise through the insulating sheet, by the gate action of the sheet;

FIG. 2 shows how a semiconductor support can carry the insulator sheet, while a belt of insulating material is rotated in contact with the support while having a charge produced thereon by a brush; and

FIG. 3 shows how the invention can be applied in a machine where an insulating image sheet is passed between a roller with a charged surface and a developer roller.

As shown in FIG. 1 (A), a base 1 supports on it an image sheet 2 of insulating material having an embedded photoconductor therein to intensify the dielectric action. A projector 3 generates a line which modifies the image sheet 2 by changing the dielectric constant of the image sheet where the light strikes. Such a sheet can now act as a gate to control the passage through it of a field applied to the back of the sheet.

The field is generated by simply rubbing an insulator sheet 4 (FIG. 1 (B) as it rests on a base 5, with a brush 6. Alternatively, the charge can be applied by a brush or semiconductor having a potential of 50 to 500 volts D.C. between it and the base 5.

The sheet 2 is now placed on the charged sheet 4 and a developer roller 7 is run over the sheet 2 to develop the areas of the sheet 2 where the charge from the sheet 4 permeates the sheet 2 to the upper surface.

The roller 7 can be formed of a pervious material dipped into or charged with a liquid developer comprising a carrier liquid and marking particles supported therein.

It is of interest to note that as the image charge is not held on the upper surface of the sheet 2 as in conventional xerography, the developer liquid need not be highly insulating as the charge from the sheet 4 can continue to extend through the image sheet from the charged sheet and is not destroyed as in present systems because of the interposed relatively insulating sheet 2 between the charge source, that is the sheet 4, and the developer roller 7.

In FIG. 2, the image sheet is designated 10, the semiconductor support 11 and the charging belt 12. The semiconductor support could be paper, and thus for instance a paper web could have an insulator coating on one side and could then be in contact with the charging belt on one side, preferably the paper side, while development takes place on the other side thereof.

The belt 12 passes around rollers 13 and is driven at high speed.

A brush 14 contacts the belt for triboelectric charging of the belt, while a developer roller 15 is arranged to pass over the image sheet.

In FIG. 3, the image sheet 18 is passed between a rol- Ier 19, which has an insulator surface, and a developer roller 20 which dips into liquid developer 21 in a tank 22. The rollers 19 and 20 rotate synchronously so far as their peripheries are concerned, and roller 19 is charged triboelectrically by rubbing contact with a rotating brush 23.

The insulating sheet which is modified to give it an imagewise dielectric pattern can be any relatively thin exposure to light or X-rays or other electromagnetic waves, particularly where a photoconductor is embedded, such electromagnetic waves making the lightstruck areas differentially conductive relative to the unmodified surface, and thus allowing such a surface to control electrical flow through such a surface at modified areas.

As the dielectrically modified surface is itself not suitable for development, it is necessary to apply a charge to one side of it while developing the other side, and as the charge applied to the image sheet can have a particular polarity, development is possible by normal xerographic developers, particularly the controlled liquid developers such as where pigment particles are coated with a resin or similar insulating control medium which are suspended in a carrier liquid having an electrical resistivity in excess of Ohm centimeter and a dielectric constant less than 3. Such developers are so well known that formulations need not be given herein.

However, as stated earlier, dielectrically sensitive developers are generally preferred for this process, and therefore some examples are appended hereto, but it is to be clear that these are merely to give a general indication of useable developers and are not in any way to be taken as limiting the invention to the examples referred to.

SHEETS OR FILMS As examples of a suitable sheet which can be dielectrically modified we find the following effective; cellulose acetate, cellulose triacetate, polymethyl methacrylate, polyethylene, or an ethylene vinyl acetate copolymer, but other insulator sheets having a dielectric constant of from 2 to 8 but preferably about 3 have been found suitable.

In the case of films with a distributed photoconductor, the true photoconductors such as hexagonal selenium and cadmium selenide are particularly effective.

The backing sheet to carry the charge preferably has a dielectric constant less than 2 and can be a thin-layer polyester or a film such as polyvinyl butyrate.

DEVELOPERS Ex mp e These materials are ground in a ball mill to form a concentrate which is then dispersed in lsopar G, in the proportions of 5 grams of Concentrate to 1 litre of Isopar G.

Example 2 24 grams of an organic black pigment such as Monolite fast Black 8.8. manufactured by I.C.I. ANZ Ltd. of Australia, Colour Index No. 50440 (an aniline black).

18 grams of a styrene-butadiene copolymer, such as Solprene 1205, manufactured by Phillips Imperial Chemical Ltd. (N.S.W. Australia).

sr m f a x ay 9 en y etss a9 men u as Pliolite VTAC, manufactured by Goodyear International Corporation of U.S.A. (Aust. distributors, Australia Synthetic Rubber Ltd.). 7

30 millilitres of aromatic hydrocarbon solvent, such as Solvesso 100, manufactured by Esso Chemical (Aust.) Ltd. to form a concentrate which is then dispersed in Isopar G, in the proportions of 5 grms. of concentrate to 1 litre of Isopar 6.38

Example 3 200 grams of a copolymer resin-coated Carbon black, such as Microlith Black C.T., manufactured by C.I.B.A. (Switzerland).

grams of a styrene-butadiene copolymer, such as Solprene I205, manufactured by Phillips Imperial Chemicals Ltd. (N.S.W. Australia).

25 grams of vinyl toluene/acrylate copolymer resin such as Piolite VTAC, manufactured by Goodyear International Corporation U.S.A. (Australian Synthetic Rubber Ltd., distributors).

300 millilitres of an aromatic hydrocarbon liquid such as Solvesso 100, manufactured by Esso Chemicals (Aust.) Ltd.

These materials are ground together in a ball mill to form a concentrate which is then dispersed in Isopar G, in the proportions of 5 grams of Concentrate to 1 litre of Isopar G.

The following examples show how concentrates can be made up which are dispersed in a carrier liquid which has an insulating value sufficiently high not to materially influence developer particle movement in an electrical field. Usually the carrier liquid has electrical resistivity exceeding l0 Ohm centimeter and a dielectric constant less than 3 but with a field which is not a latent image field as in the present case this could be somewhat lower say l0 Ohm centimeter as a stronger field can be used.

The preferred carrier liquids are however the hydrocarbon marketed under the trade mark Isopar G, or alternatively a solvent such as Shell solvent X4 or that marketed under the trade mark Shellsol T. The ingredients of the following examples are milled together to form a paste which is then suitable for storage and subsequent adding to a carrier liquid.

Example 4 2 grams Myristic acid (The British Drug Houses) 20 grams Isopar G 3 grams Potassium Permanganate (The British Drug Houses).

Example 3 grams Aluminium Oxide, as sold under the trade mark 600 Alundum (Norton Abrasive CO.).

2 grams Maise Oil.

Example 6 1 gram Nigrosine water soluble (The British Drug Houses).

3 grams Tung Oil.

Example 7 5 grams Chrome Alum (pure). 2 grams Mineral Oil.

Example 8 5 grams Black Manganese Dioxide. 2 grams Linseed Oil Varnish.

Example 9 1 gram Phenol Red (Fisher Scientific Co.)

1 gram Safflower Oil (Meggitts).

We claim:

1. A method of recording on the surface of an insulator medium an image, comprising modifying the insulator medium by electromagnetic waves to change the dielectric constant thereof at selected areas to produce a dielectric image, placing the thusly modified insulator medium on a member having a latent uniform electric field thereon thereby applying a uniform field through the insulator medium from one side of the said insulator surface, and simultaneously applying a developer to the other side of the said surface, whereby the insulator medium acts to control the uniform field in accordance with the dielectric constant at said selected areas.

2. The method according to claim 1 comprising embedding a photoconductor in the said insulator medium.

3. The method according to claim 1 wherein the electric field is applied from an insulating member which has been charged triboelectrically.

4. The method according to claim 1 wherein the electric field is applied from an insulating member which is charged by friction rubbing.

5. The method according to claim 1 wherein the electric field is applied from a DC. voltage source by passing a charging member connected to said source over an insulating member supported on a conductive back also connected with said voltage source.

6. The method of claim 1 wherein the thusly modified medium has a dielectric constant in excess of 2 at 10 CR8.

7. A method according to claim 1 wherein the thusly modified medium is cellulose acetate, cellulose triacetate, polymethyl methacrylate, polyethylene, ethylene vinyl acetate copolymer, or polyvinyl butyrate.

8. The method of claim 1 wherein said member has a dielectric constant less than 2 at 10 CPS.

9. The method according to claim 1 wherein said member comprises a polyester film.

10. The method according to claim 1 wherein said developer comprises marking particles with an insulating surface, suspended in an electrically insulating liquid.

11. The method according to claim 1 wherein the I image is developed by a dielectrically sensitive developer.

12. The method according to claim 1 wherein said developer comprises polar particles suspended in an electrically insulating liquid.

13. The method according to claim 1 wherein said developer comprises a pigment and a copolymer suspended in an insulating liquid.

14. The method according to claim 1 wherein the said developer comprises a pigment and a styrenebutadiene copolymer suspended in an insulating liquid.

15. The method according to claim 1 wherein the said developer comprises a copolymeric resin-coated pigment and a styrenc-butadiene copolymer formed as a paste and suspended in an insulating liquid.

16. The method according to claim 1 wherein said developer comprises a pigment and vinyl toluene/acrylate copolymer formed as a paste and suspended in an insulating liquid.

17. The method according to claim 1 wherein said developer comprises a pigment and a styrenebutadiene copolymers and a vinyl toluene/acrylate copolymer formed as a paste and suspended in an insulating liquid.

18. The method according to claim 1 wherein said developer comprises myristic acid and potassium permanganate suspended in an insulating carrier liquid.

19. The method according to claim 1 wherein the developer comprises pigment particles of aluminum oxide or water soluble nigrosine or chrome alum or manganese dioxide, ground with an oil to form a paste and suspended in an insulating carrier liquid. 

2. The method according to claim 1 comprising embedding a photoconductor in the said insulator medium.
 3. The method according to claim 1 wherein the electric field is applied from an insulating member which has been charged triboelectrically.
 4. The method according to claim 1 wherein the electric field is applied from an insulating member which is charged by friction rubbing.
 5. The method according to claim 1 wherein the electric field is applied from a D.C. voltage source by passing a charging member connected to said source over an insulating member supported on a conductive back also connected with said voltage source.
 6. The method of claim 1 wherein the thusly modified medium has a dielectric constant in excess of 2 at 103 C.P.S.
 7. A method according to claim 1 wherein the thusly modified medium is cellulose acetate, cellulose triacetate, polymethyl methacrylate, polyethylene, ethylene vinyl acetate copolymer, or polyvinyl butyrate.
 8. The method of claim 1 wherein said member has a dielectric constant less than 2 at 103 CPS.
 9. The method according to claim 1 wherein said member comprises a polyester film.
 10. The method according to claim 1 wherein said developer comprises marking particles with an insulating surface, suspended in an electrically insulating liquid.
 11. The method according to claim 1 wherein the image is developed by a dielectrically sensitive developer.
 12. The method according to claim 1 wherein said developer comprises polar particles suspended in an electrically insulating liquid.
 13. The method according to claim 1 wherein said developer comprises a pigment and a copolymer suspended in an insulating liquid.
 14. The method according to claim 1 wherein the said developer comPrises a pigment and a styrene-butadiene copolymer suspended in an insulating liquid.
 15. The method according to claim 1 wherein the said developer comprises a copolymeric resin-coated pigment and a styrene-butadiene copolymer formed as a paste and suspended in an insulating liquid.
 16. The method according to claim 1 wherein said developer comprises a pigment and vinyl toluene/acrylate copolymer formed as a paste and suspended in an insulating liquid.
 17. The method according to claim 1 wherein said developer comprises a pigment and a styrene-butadiene copolymers and a vinyl toluene/acrylate copolymer formed as a paste and suspended in an insulating liquid.
 18. The method according to claim 1 wherein said developer comprises myristic acid and potassium permanganate suspended in an insulating carrier liquid.
 19. The method according to claim 1 wherein the developer comprises pigment particles of aluminum oxide or water soluble nigrosine or chrome alum or manganese dioxide, ground with an oil to form a paste and suspended in an insulating carrier liquid. 